1. Field of the Invention
The present invention relates to a thruster which produces thrust by spurting out a gas produced by decomposition reaction of a propellant such as hydrazine and a spacecraft equipped with the thruster.
2. Description of the Related Art
Spacecraft such as artificial satellites and rockets are equipped with thrusters for controlling attitude and changing orbit in outer space. Monopropellant catalytic thrusters are a type of thrusters which supply a propellant such as hydrazine from a tank to a catalyst layer via a propellant valve and an injector to cause the propellant to decompose on the catalyst layer, and spurt out a gas resulting from the decomposition through a nozzle, thereby producing thrust.
The life of the thrusters for controlling attitude and orbit of the spacecraft is so crucial that it may possibly determine the life of the spacecraft itself. It is required that the thrusters be trouble-free and resistant to repeated use over a long period of time in special circumstances of the outer space.
With regard to thrusters of this type, a technology has been developed which prevents local degradation that the catalyst undergoes in the decomposition reaction when the propellant is supplied to the catalyst layer through an extra fine tube connected to the propellant valve, and improves the responsiveness and safety of the propellant valve (see JP 2009-257155 A, referred to as patent document 1).
The technology disclosed in patent document 1 can increase the life of the catalyst itself. The thrusters, however, generally have a problem that the catalyst layer reaches high temperature in the decomposition reaction, where heat is conducted from a chamber that holds the catalyst layer to the whole thruster, and to the structure of the spacecraft to which the thruster is attached.
For example, in a monopropellant thruster using hydrazine as a propellant and a catalyst layer formed of alumina particles coated with iridium which is a catalyst, the temperature of the propellant valve needs to be limited to about 120° C. while the catalyst layer reaches as high temperature as about 900° C.
To meet this requirement, the catalyst layer-holding chamber is made of a cobalt-nickel alloy resistant to high temperature, and a thermal-insulating structure is provided between the chamber and the propellant valve. However, the cobalt-nickel alloy does not have a high thermal insulating capability, and thus, it is difficult to reduce transfer of heat to the propellant valve and to the spacecraft structure. In addition, a heater is provided to preheat the catalyst layer and keep the propellant valve at appropriate temperature, where lower thermal insulation performance between the chamber and the propellant valve leads to greater power consumption of the heater.